- have Shatner return to his shorter, better kept season one haircut...

But 1968 was not 1966. The actors in virtually any TV series that encompassed both years would have longer hair in 1968. Neither Shatner nor the behind-the-scenes staff would have seen anything wrong with Kirk having longer hair too; note also that the one "futuristic" element of the men's hairstyles on the show (the pointed sideburns) also became longer and bushier in the third season. At least Spock's hair wasn't longer...